The following description relates to testing of communications devices, and more particularly to testing of communications devices with non-deterministic latency.
A communications device may be configured to transmit and receive data using a communications medium. For example, a SONET transceiver or framer may transmit and receive data using an optical network including microwave, coaxial, twisted pair, and fiber optic connections. The SONET transceiver may include a number of analog circuits, such as, for example, an automatic gain control circuit, an equalizer, a phase-locked loop, and a data recovery circuit. A SONET framer may include a number of first-in, first-out buffers (FIFOs). Data may be received at a line side of the transceiver or framer and output to a system side of the transceiver or framer.
Because the transceiver includes a number of analog circuits, and the framer includes a number of FIFOs, SONET communications devices do not have a predictable signal propagation time/phase alignment between the line side and the system side. In other words, the data that travel through the communications device have a non-deterministic latency between the time the data are received and the time that the data are output.
A communications device may be tested to verify operational performance, to certify that the device satisfies operational standards and specifications, and to ensure the quality of the device before the device is shipped or installed. When testing a communications device, a testing machine may inject or input a test data payload in the line side of the device, and receive processed test data on the system-side of the device. However, if the communication device has a non-deterministic latency between the line side and the system side, then data output at the system side after being input to the communications device must be processed to determine where a desired data portion (e.g., a data packet) in the output data is located.
The processing needed to locate a desired data portion adds a delay to the total time needed to test each communications device. As a result, the time required to test each device may be significant when testing a large number of devices.
Like reference symbols in the various drawings indicate like elements.